abstract class LLMS_Abstract_User_Data {

	/**
	 * Student's WordPress User ID
	 *
	 * @var int
	 */
	protected $id;

	/**
	 * User postmeta key prefix
	 *
	 * @var  string
	 */
	protected $meta_prefix = 'llms_';

	/**
	 * Instance of the WP_User
	 *
	 * @var obj
	 */
	protected $user;

	/**
	 * Constructor.
	 *
	 * By default, the current user is loaded if no `$user` is supplied. This behavior can be disabled by providing `$autoload = false`.
	 *
	 * @since 2.2.3
	 * @since 3.9.0 Unknown.
	 * @since 7.0.0 Added `$autoload` parameter.
	 *
	 * @param int|null|WP_User|LLMS_Abstract_User_Data $user     A `WP_User` ID, instance of a `WP_User`, or instance of any class extending this class.
	 * @param boolean                                  $autoload If `true` and `$user` input is empty, the user will be loaded from `get_current_user_id()`.
	 *                                                           If `$user` is not empty then this parameter has no impact.
	 * @return void
	 */
	public function __construct( $user = null, $autoload = true ) {

		$user = ( $user || $autoload ) ? $this->get_user_id( $user ) : false;
		if ( false !== $user ) {
			$this->id   = $user;
			$this->user = get_user_by( 'ID', $user );
		}

	}

	/**
	 * Magic Getter for User Data
	 *
	 * Mapped directly to the WP_User class.
	 *
	 * @since 3.0.0
	 * @since 3.10.1 Unknown.
	 * @since 3.34.0 Allow `user_url` to be retrieved.
	 *
	 * @param    string $key key of the property to get a value for
	 * @return   mixed
	 */
	public function __get( $key ) {

		// Array of items we should *not* add the $this->meta_prefix to.
		$unprefixed = apply_filters(
			'llms_student_unprefixed_metas',
			array(
				'description',
				'display_name',
				'first_name',
				'last_name',
				'nickname',
				'user_login',
				'user_nicename',
				'user_email',
				'user_registered',
				'user_url',
			),
			$this
		);

		/**
		 * Add the meta prefix to things that aren't in the above array
		 * only if the meta prefix isn't already there
		 * this means that the following will output the same data
		 * $this->get( 'llms_billing_address_1')
		 * $this->get( 'billing_address_1')
		 */
		if ( false === strpos( $key, $this->meta_prefix ) && ! in_array( $key, $unprefixed ) ) {
			$key = $this->meta_prefix . $key;
		}

		if ( ! $this->exists() ) {
			return '';
		}

		return apply_filters( 'llms_get_student_meta_' . $key, $this->user->get( $key ), $this );

	}

	/**
	 * Retrieve an item from the cache
	 *
	 * @param    string $key   cache key
	 * @return   false|mixed       false on failure
	 * @since    3.17.0
	 * @version  3.17.0
	 */
	protected function cache_get( $key ) {
		return wp_cache_get( $key, $this->get_cache_group() );
	}

	/**
	 * Delete an item from the cache
	 *
	 * @param    string $key  cache key
	 * @return   bool
	 * @since    3.17.0
	 * @version  3.17.0
	 */
	protected function cache_delete( $key ) {
		return wp_cache_delete( $key, $this->get_cache_group() );
	}

	/**
	 * Add an item to the cache cache
	 *
	 * @param    string $key  cache key
	 * @param    mixed  $val  value to cache
	 * @return   boolean
	 * @since    3.17.0
	 * @version  3.17.0
	 */
	protected function cache_set( $key, $val ) {
		return wp_cache_set( $key, $val, $this->get_cache_group() );
	}

	/**
	 * Determine if the user exists
	 *
	 * @return   boolean
	 * @since    3.9.0
	 * @version  3.9.0
	 */
	public function exists() {
		return ( $this->user && $this->user->exists() );
	}

	/**
	 * Allows direct access to WP_User object for retrieving user data from the user or usermeta tables
	 *
	 * @since   3.0.0
	 * @version 3.0.0
	 * @param   string $key key of the property to get a value for
	 * @return  mixed
	 */
	public function get( $key ) {
		return $this->$key;
	}

	/**
	 * Retrieve the group name used by cache functions
	 *
	 * @return   string
	 * @since    3.17.0
	 * @version  3.17.0
	 */
	protected function get_cache_group() {
		return sprintf( 'llms_user_%d', $this->get( 'id' ) );
	}

	/**
	 * Retrieve the user id
	 *
	 * @since 3.9.0
	 * @since 4.2.0 Always return an absolute integer.
	 *
	 * @return int
	 */
	public function get_id() {
		return absint( $this->id );
	}

	/**
	 * Allow extending classes to access the main student class
	 *
	 * @return   LLMS_Student|false
	 * @since    3.9.0
	 * @version  3.9.0
	 */
	protected function get_student() {
		return llms_get_student( $this->get_id() );
	}

	/**
	 * Retrieve the instance of the WP User for the student
	 *
	 * @return   WP_User
	 * @since    3.9.0
	 * @version  3.9.0
	 */
	public function get_user() {
		return $this->user;
	}

	/**
	 * Retrieve the User ID based on object
	 *
	 * @param    mixed $user  WP_User ID, instance of WP_User, or instance of any student class extending this class
	 * @return   mixed            int if a user id can be found, otherwise false
	 * @since    3.9.0
	 * @version  3.9.0
	 */
	protected function get_user_id( $user ) {

		if ( ! $user && get_current_user_id() ) {
			return get_current_user_id();
		} elseif ( is_numeric( $user ) ) {
			return $user;
		} elseif ( is_a( $user, 'WP_User' ) && isset( $user->ID ) ) {
			return $user->ID;
		} elseif ( $user instanceof LLMS_Abstract_User_Data ) {
			return $user->get_id();
		}

		return false;

	}

	/**
	 * Update a meta property for the user
	 *
	 * @param    string  $key     meta key
	 * @param    mixed   $value   meta value
	 * @param    boolean $prefix  include the meta prefix when setting
	 *                            passing false will allow 3rd parties to update fields with a custom prefix
	 * @since    3.2.0
	 * @version  3.2.0
	 */
	public function set( $key, $value, $prefix = true ) {
		$key = $prefix ? $this->meta_prefix . $key : $key;
		update_user_meta( $this->get_id(), $key, $value );
	}

}